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The paleobiogeography of hominoids exhibits a puzzling pattern of migrations between and within Africa and Eurasia. A precise dating of hominoid-bearing localities is therefore essential to reveal the timing, direction and possible causes of dispersals. Here, we present a bio-magnetostratigraphic analysis of the section of Engelswies (Southern Germany, Upper Freshwater Molasse, North Alpine Foreland Basin) where the oldest Eurasian hominoid was found. Our paleomagnetic results reveal a very short normal and a reverse magnetic polarity for the entire section. The polarity record is correlated to the Astronomical Tuned Neogene Time Scale using an integrated stratigraphic approach. This approach follows the chronostratigraphic framework for the Upper Freshwater Molasse, which combines magnetostratigraphy with biostratigraphic, lithostratigraphic and 40 Ar/ 39 Ar dating results. According to this outcome, the reverse polarity of the Engelswies section most likely correlates to magnetochron C5Cr. The origin of the short normal polarity remains enigmatic. The magnetostratigraphic calibration and the evolutionary level of the Engelswies small mammal fauna suggest an age of 17.1–17.0 Ma (Early Karpatian, Early Miocene) for the oldest Eurasian hominoid, and roughly confirm the estimates of Heizmann and Begun (2001) . The estimated age suggests that the first hominoids in Eurasia are contemporaneous with Afro-Arabian afropithecins, and dispersal may have been facilitated by intra-Burdigalian (∼18–17 Ma) sea-level low stands and the beginning of the Miocene Climate Optimum. The paleoclimatic and environmental reconstruction of the Engelswies locality indicates a lakeshore environment near dense subtropical rain forest vegetation, where paratropical temperatures (mean annual temperature around 20 °C) and humid conditions (mean annual precipitation > 1.100 mm) prevailed.

A detailed integrated stratigraphic study (biostratigraphy and magnetostratigraphy) was carried out on five sections from the western part of the Bavarian Upper Freshwater Molasse of the North Alpine Foreland Basin (NAFB), greatly improving the chronostratigraphy of these sediments. The sections belong to the lithostratigraphic units Limnische Untere Serie (UL) and Fluviatile Untere Serie (UF) and contain 19 (mostly new) small-mammal bearing levels, significantly refining the local biostratigraphy. Radiometric ages obtained from glass shards from tuff horizons are used together with the biostratigraphic information for constructing and confirming the magnetostratigraphic correlation of the studied sections to the Astronomical Tuned Time Scale (ANTS04; Lourens et al. in Geologic Time Scale 2004, Cambridge University Press, 2004). This correlation implies that the UL lithostratigraphic unit corresponds to the latest Ottnangian and the Early Karpatian, whereas the UF corresponds to the Karpatian and the Early Badenian. This indicates that the Brackish- to Freshwater Molasse transition already occurred during the late Ottnangian. The pre-Riesian hiatus occurred in the latest Karpatian and lower Early Badenian in Eastern Bavaria and Bohemia and in the Late Karpatian and earliest Badenian in Western Bavaria. The geochemical and Ar-Ar data of volcanic ashes suggest that highly evolved silicic magmas from a single volcano or volcanic center, characterized by a uniform Nd isotopic composition, erupted repetitively over the course of at least 1.6 Myr. Three phases of eruptive activity were identified at 16.1 ± 0.2 Ma (Zahling-2), 15.6 ± 0.4 Ma (Krumbad), and 14.5 ± 0.2 Ma (Heilsberg, Hegau). The correlation of the local biostratigraphic zonation to the ANTS04 enables further the characterization of both the Ottnangian-Karpatian and Karpatian-Badenian boundaries in the NAFB by small-mammal biostratigraphy. According to these results the Ottnangian-Karpatian boundary is contemporaneous with the first appearance datum of Megacricetodonbavaricus (in the size of the type population) and the first common occurrence of Keramidomys thaleri, whereas Ligerimys florancei, Melissiodon dominans and Prodeinotherium aff. bavaricum have been already disappeared during the late Ottnangian. The Karpatian-Badenian boundary is characterized by a significant size increase of the large Megacricetodon lineage and possibly a (re-)immigration of Prodeinotherium bavaricum.

article i nfo The middle Miocene Valdearenas-Muduex section in the internally-drained, continental Madrid Basin (central Spain) is dated bio-magnetostratigraphically between 15.2 Ma and 11.5 Ma. The section contains two formation-scale, sedimentary sequences, that both consist of a siliciclastic lower part and a calcareous upper part. Siliciclastic sedimentation took place in distal floodplain and fluvial environments, while limestones resulted from carbonate precipitation in calcic soil profiles and in ephemeral lacustrine water bodies. Spectral analysis of the L* colour time series points to the influence of the ∼405-kyr and 0.97-Myr eccentricity cycles, while the bases of the two calcareous intervals correlate to successive minima of the 2.4-Myr eccentricity cycle. The 405-kyr cycle lags maximum eccentricity, whereas the 0.97 and 2.4-Myr cycleslag minimum eccentricity, each by approximately a quarter of a cycle. No obliquity forcing isdetected. The observed orbital configuration of 2.4-Myr minima at the base of limestone-dominated intervals is similar to a previously documented Late Miocene shift in the Teruel Basin of northeast Spain. Our results indicate that long-period eccentricity clim ate forcing may well be as ignificant player on long, tectonic time scales in continental basin fill.

Upper Miocene mudflat and marginal lacustrine sediments were deposited on the fringes of an alluvial-fan system in the low-gradient, endorheic southern Teruel Basin, northeast Spain. The 147-m-thick Prado succession consists of 55 meter-scale sedimentary cycles, displaying a clastic-rich and a carbonate-rich interval. The clastic-rich parts are weakly pedogenically modified, red to yellow-orange mudstones and are interpreted as deposits of a well-drained mudflat. The carbonate-rich sediments consist of calcretes, marls, and muddy limestones. The calcretes range from dispersed nodules to massive nodular and are interpreted to be of pedogenic or phreatic origin. The marls and muddy limestones are light- to dark-gray and rich in organic matter, shell fragments, and gastropods. They are interpreted as ephemeral pond to marginal lacustrine deposits. A composite sedimentary cycle model is presented summarizing the different facies and their vertical distribution throughout the Prado area. On a 10 m scale, distinct stratigraphic intervals show lithologic trends representing alternating wetter and drier paleoenvironments. Cycle characteristics are laterally consistent, whereby limestone beds pinch out towards the basin margin and thicken towards the central parts of the 10-km-wide and 20-km-long subbasin. The high-resolution magnetostratigraphy resolves four normal-polarity and four reversed-polarity intervals that are straightforwardly correlated to chron interval C5n.2n to C5Ar.1r in the ATNTS04 time scale. The resulting age control indicates a duration of 19 to 23 kyr for the meter-scale lithofacies cycles, suggesting control by precession-driven climate change. An astronomical tuning is established by correlating each cycle to the La2004 precession curve using recently recalibrated ages for the polarity reversals as a starting point. The resulting astronomical ages for the reversals in the Prado section are consistent with the astronomically calibrated magnetostratigraphy and cyclostratigraphy of the marine Monte dei Corvi section in Italy. At Prado, three intervals with thicker-than-average cycle thickness most likely reflect obliquity influence during 405 kyr eccentricity minima when precession amplitudes are low. This corroborates the orbital forcing hypothesis of the lithofacies cycles and the astronomical tuning of the Prado succession. The combined magnetostratigraphy and cyclostratigraphy method applied in this study shows the high potential of this method for detecting orbital climate forcing in continental successions.

International audience; Pollen and paleomagnetic analysis of the Rubielos de Mora-1 core (Rubielos de Mora basin, NE Spain) has been carried out with the aim of reconstructing floral, vegetational and climatic changes within an accurate time framework. Based on biostratigraphic information, the magnetostratigraphy (ATNTS04) resulting in an age of Early Miocene for the cored sedimentary sequence. The high percentages of thermophilous taxa and the diverse subarid flora in the pollen spectra points to a very dry subtropical climate with a marked seasonality, reflecting the onset of the Miocene climatic optimum. On the other hand, taxa with high water requirements (riparian) are also abundant. Alternation in pollen taxa (thermophilous vs. mesothermic–riparian), coincide with sedimentological changes, which are related to lake level fluctuations and vegetation changes. In turn, the vegetational pattern indicates cyclic changes in temperature and precipitation which is controlled by astronomically forced obliquity cycles.

We present an integrated stratigraphic study of cyclically bedded distal alluvial fan to lacustrine deposits in the late Miocene continental sections of Cascante and Canizar (Teruel basin, NE Spain). The cyclostratigraphic analysis reveals that different scales of sedimentary cyclicity are present with a thickness ratio of about 1:2:5. Spectral analysis of colour records in the depth domain indicates the presence of a significant peak at ∼2.2 m, which corresponds to the average thickness of the basic, mudstone–carbonate, cycle. Other peaks correspond to the large-scale cycle, which consists of clusters of five basic cycles, and to a cycle twice the average thickness of the basic cycle. Magnetostratigraphic results, in combination with small-mammal biostratigraphy, indicate that the three normal polarity intervals recorded in our sections correspond to C5n.2n, C5n.1n and C4Ar.2n. Assigning the ages of CK95 to the polarity reversals implies significant changes in sedimentation rate, which is not in agreement with the regularity of the sedimentary cyclicity. Thus, spectral analysis of high-resolution colour records in the time domain only produce a spectrum that is consistent with Milankovitch climate forcing, if several of the assigned age tie points are excluded. This indicates that the sedimentary cyclicity in these sections is related to astronomical variations in climate and that the ages of reversal boundaries are in error. Hence, we have calculated the astronomical durations for C4Ar.2n (87 ky), C4Ar.3r (54 ky), C5n.1n (141 ky), and C5n.1r (33 ky), which indeed show significant discrepancies with CK95. The duration pattern of our polarity intervals is confirmed by seafloor anomaly profiles and magnetostratigraphic records of deep-sea cores. Consequently, this study demonstrates that astronomically forcing in continental sequences can be a powerful tool to improve the fundamental dating of the geological record.

The middle Miocene sedimentary fill of the Calatayud Basin in north-eastern Spain consists of proximal to distal alluvial fan-floodplain and shallow lacustrine deposits. Four main facies groups characteristic of different sedimentary environments are recognized: (1) proximal and medial alluvial fan facies that comprise clast-supported gravel and subordinate sandstone and mudstone, the latter exhibiting incipient pedogenic features; (2) distal alluvial fan facies, formed mainly of massive mudstone, carbonate-rich palaeosols and local carbonate pond deposits; (3) lake margin facies, which show two distinct lithofacies associations depending on their distribution relative to the alluvial fan system, i.e. front (lithofacies A), comprising massive siliciclastic mudstone and tabular carbonates, or lateral (lithofacies B) showing laminated and/or massive siliciclastic mudstone alternating with tabular and/or laminated carbonate beds; and (4) mudflat–shallow lake facies showing a remarkable cyclical alternation of green-grey and/or red siliciclastic mudstone units and white dolomitic carbonate beds. The cyclic mudflat–shallow lake succession, as exposed in the Orera composite section (OCS), is dominantly composed of small-scale mudstone–carbonate/dolomite cycles. The mudstone intervals of the sedimentary cycles are interpreted as a result of sedimentation from suspension by distal sheet floods, the deposits evolving either under subaerial exposure or water-saturated conditions, depending on their location on the lacustrine mudflat and on climate. The dolomite intervals accumulated during lake-level highstands with Mg-rich waters becoming increasingly concentrated. Lowstand to highstand lake-level changes indicated by the mudstone/dolomite units of the small-scale cycles reflect a climate control (from dry to wet conditions) on the sedimentation in the area. The spatial distribution of the different lithofacies implies that deposition of the smallscale cycles took place in a low-gradient, shallow lake basin located in an interfan zone. The development of the basin was constrained by gradual alluvial fan aggradation. Additional support for the palaeoenvironmental interpretation is derived from the isotopic compositions of carbonates from the various lithofacies that show a wide range of δ18O and δ13C values varying from )-7.9 to 3.0‰ PDB and from -9.2 to -1.7‰ PDB respectively. More negative δ18O and δ13C values are from carbonate-rich palaeosols and lakemargin carbonates, which extended in front of the alluvial fan systems, whereas more positive values correspond to dolomite beds deposited in the shallow lacustrine environment. The results show a clear trend of δ18O enrichment in the carbonates from lake margin to the centre of the shallow lake basin, thereby also demonstrating that the lake evolved under hydrologically closed conditions.

The Milankovitch theory of climate change is widely accepted, but the registration of the climate changes in the stratigraphic record and their use in building high-resolution astronomically tuned timescales has been disputed due to the complex and fragmentary nature of the stratigraphic record. However, results of time series analysis and consistency with independent magnetobiostratigraphic and/or radio-isotopic age models show that Milankovitch cycles are recorded not only in deep marine and lacustrine successions, but also in ice cores and speleothems, and in eolian and fluvial successions. Integrated stratigraphic studies further provide evidence for continuous sedimentation at Milankovitch time scales (104 years up to 106 years). This combined approach also shows that strict application of statistical confidence limits in spectral analysis to verify astronomical forcing in climate proxy records is not fully justified and may lead to false negatives. This is in contrast to recent claims that failure to apply strict statistical standards can lead to false positives in the search for periodic signals. Finally, and contrary to the argument that changes in insolation are too small to effect significant climate change, seasonal insolation variations resulting from orbital extremes can be significant (20% and more) and, as shown by climate modelling, generate large climate changes that can be expected to leave a marked imprint in the stratigraphic record. The tuning of long and continuous cyclic successions now underlies the standard geological time scale for much of the Cenozoic and also for extended intervals of the Mesozoic. Such successions have to be taken into account to fully comprehend the (cyclic) nature of the stratigraphic record.

In the astronomically tuned Miocene continental Orera Composite Section (OCS) of NE Spain, one short interval and two single sample levels of normal polarity were found. The low sampling resolution inhibited determination of whether these normal polarity intervals represent remagnetization, reversal excursions or even short subchrons. We have sampled these intervals with high resolution, to determine their authenticity, and their astronomical duration. Rock magnetic analysis indicates that the main magnetic minerals in the studied rocks are magnetite and (fine-grained) hematite. Furthermore, a positive correlation is observed between rock magnetic parameters and lithology. Geochemical analysis also reveals a strong relation between concentrations of the main elements Al, Ca and Mg and lithologic changes. To characterize the sedimentary environment and possibly identify diagenetic influence on acquisition of the natural remanent magnetization (NRM), multivariate classification techniques were performed using both geochemical and rock magnetic variables. We conclude that the short polarity intervals-denoted as OCS-1, OCS-2 and OCS-3-are not overprints or artefacts of diagenetic processes, but represent real features of the geomagnetic field. The normal polarity interval OCS-1 has an estimated duration of 26 kyr, and corresponds to cryptochron C5r.2r-1 identified at ODP Site 845. We argue that it must now be termed as subchron C5r.2r-ln. OCS-2 has a duration of 15 kyr, and although it does not clearly show a pair of reversals, it must be denoted as subchron C5r.2r-2n. Finally, OCS-3 has a duration of 9 kyr, a full pair of reversals and must be considered as subchron C5r.3r-1n.

Results are presented of a detailed carbonate petrographic study of an Upper Miocene lacustrine mixed carbonate-siliciclastic succession in the Teruel Basin (Spain) with the aim of constraining lake-level variability at different stratigraphic scales. Regular alternations of red to green mudstone and lacustrine limestone, termed the 'basic cycle', reflect lake-level variations at the metre-scale. In an earlier study, the basic cycle was shown to be controlled by the climatic precession cycle. Petrographic analysis made it possible to distinguish two main carbonate microfacies groups characteristic of very shallow transient and shallow permanent lake environments, respectively. In addition to the basic cyclicity, the microfacies analysis reveals lake-level variations on a larger scale. As a consequence, the astronomical forcing hypothesis of the cyclicity in the Cascante section is explored further. A climate modelling study of orbital extremes indicates that high lake levels could relate to enhanced net winter precipitation and runoff during precession minima, consistent with Mediterranean geological data. Using this phase relationship, an astronomical tuning of the cycles is established starting from astronomical ages of magnetic reversal boundaries. Subsequently, successive basic cycles are correlated to precession minima. The tuning reveals an identical number of basic cycles in the Cascante section as precession-related sapropel cycles in the deep marine succession at Monte dei Corvi (Italy), corroborating the precessional control of the basic cycles at Cascante. Lake-level highstands in the large-scale cycle identified by the microfacies analysis relate to maxima in both the ca 100 and 405kyr eccentricity cycles, again consistent with Mediterranean geological data. Subtraction of the identified astronomically related (lake-level) variations from the palaeoenvironmental record at Cascante indicates a shift to deeper and more permanent lacustrine environments in the upper half of the section. The cause of this shift remains unclear, but it may be linked to tectonics, non-astronomical climate, long-period astronomical cycles or autogenic processes. © 2008 The Authors. Journal compilation © 2008 International Association of Sedimentologists.

International audience; Pollen analysis of a Lower Miocene succession from the Rubielos de Mora Basin (NE Spain) has been carried out with the aim of reconstructing the flora, vegetation and climatic changes. Previous paleobotanical studies on these sedimentary rocks and adjacent areas interpreted very diverse climates for the Early Miocene: from humid temperate to dry subtropical. In this study, a rich thermophilous pollen spectrum and a diverse subarid flora including Nitraria, Caesalpiniaceae, Ephedra and Acacia, indicative of a dry subtropical climate are identified. On the other hand, mesothermic taxa with high water requirements are also abundant. Therefore, the pollen assemblages evidence the juxtaposition of very contrasted environments: the presence of subdesertic taxa, typical of plants growing in the lowlands and conditioned by a long warm, dry season, together with others with very high water requirements, needing constant water. This can be explained by the presence of the Rubielos de Mora Lake providing local conditions for developing riparian forests. The vegetation was clearly controlled by the water availability under a subtropical and dry-seasonal climate. Pollen changes along the succession, which coincide with sedimentological changes, are related to climatic variations. Alternation in pollen taxa (thermophilous–dry vs. mesothermic–riparian) reflects the influence of the cyclicity of temperature and precipitation on the lake level and vegetation.

The Sarmatian/Pannonian boundary in the Central Paratethys basin is marked by a major regressive event, which isolated the basin from the open sea and resulted in a palaeoenvironmental change from restricted marine to brackish water ecosystems. The exact age of this environmental change is still ambiguous since direct age control on the boundary interval is lacking, mainly due to the scarcity of suitable sections. The Vranović section in the Našice Quarry in Croatia, however, is relatively long and continuously exposed. A detailed sedimentological and biostratigraphic study indicates that it contains the Sarmatian/Pannonian boundary and that it reflects the same palaeoenvironmental trend as other Paratethyan sequences. Here, we present palaeomagnetic and rock magnetic results from the Vranović section, based on 183 sampled levels distributed along 55 m of cyclically bedded limestones and marls. Rock magnetic data indicate the presence of maghemite or haematite in the Sarmatian deposits and low contents of magnetite in the Pannonian rocks. Thermal demagnetization results indicate dominantly normal polarities, and the mean direction closely coincides with the present-day field direction at Našice. We conclude that magnetostratigraphic age control cannot be derived for the Vranović section because of a dominant secondary (post-tilt) magnetization. Consequently, a firm numerical age based on magnetostratigraphy cannot be assigned to Sarmatian/Pannonian boundary events from this section.

Mammals are among the fastest-radiating groups, being characterized by a mean species lifespan of the order of 2.5 million years (Myr)1,2. The basis for this characteristic timescale of origination, extinction and turnover is not well understood. Various studies have invoked climate change to explain mammalian species turnover3,4, but other studies have either challenged or only partly confirmed the climate–turnover hypothesis5–7. Here we use an exceptionally long (24.5–2.5Myr ago), dense, and welldated terrestrial record of rodent lineages from central Spain, and show the existence of turnover cycles with periods of 2.4–2.5 and 1.0Myr. We link these cycles to low-frequency modulations of Milankovitch oscillations8, and show that pulses of turnover occur at minima of the 2.37-Myr eccentricity cycle and nodes of the 1.2-Myr obliquity cycle. Because obliquity nodes and eccentricity minima are associated with ice sheet expansion and cooling and affect regional precipitation, we infer that long-period astronomical climate forcing is a major determinant of species turnover in small mammals and probably other groups as well.

Sedimentary cycles may reflect orbitally induced climate oscillations and can then be used to construct astronomical time–scales. Following the initial tuning of the Late Pleistocene, the ‘anchored’ astronomical time–scale was extended to the base of the Pliocene, using palaeoclimatic records from Ocean Drilling Project (ODP) sites in the eastern equatorial Pacific and North Atlantic and sedimentary cycle patterns in marine successions exposed onland in the Mediterranean. In this paper we present a review of the progress subsequently made in establishing a Late Neogene astronomical (polarity) time–scale (A(P)TS) in the Mediterranean region. Major steps forward are (1) the evaluation of the initial time–scale, using high–resolution climatic proxy records, different astronomical solutions and the additional influence of obliquity on sedimentary cycle patterns, (2) the extension of the A(P)TS into the Middle Miocene, i.e. back to about 12 3Ma, (3) the closure of the Messinian gap in the A(P)TS, (4) the incorporation of the continental record, and (5) the intercalibration of astronomical and radioisotopic time.